Insulation



"Jan. 15, 1946. c. we". .2,393,082

INSULATION FiledJnly 29, 194s WITNESSES:

i INVENToR Conrool/s/e/ y www ATTORNEY Patented Jan. 15, 1946 INSULATION Conrad Weil, Wil-kinsburg, Pa., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application Jui'y 29, 1943, serial 10.496,57':

2 Claims.

My invention relates to commutator-type dynamo-electric machines such as direct-current motors and generators; and it has particular relation to means for preventing short-circuiting oi the amature-winding of such a machine as a result of carbon-dust deposits accumulating on the inner periphery of the commutator-terminals oi the winding, back of the commutator-necks.

Such carbon-dust accumulations result from the wear of the carbon or carbonaceous brushes which bear on the commutator, and this carbondust is deposited on all commutator-machines, particularly those machines which are ventilated with recirculated air, where the accumulation is particularly rapid. The result of such accumulations is a conducting crust which eventually extends in a continuous path between terminals of opposite polarities, resulting in a short-circuit, unless preventive measures are adopted.

The object of my invention is to provide an extremely effective means for preventing, or substantially preventing, such-carbon-dust creepagepaths, at a cost which is practically negligible, involving only a few small pieces of insulating sheetmaterial which are laid in place during the winding-operation.

My invention is illustrated in the accompanying drawing, wherein Figure 1 is a fragmentary longitudinal sectional view of a commutator-type dynamo-electric machine utilizing my invention.

Fig. 2 is a developed plan View of a portion of the lower layer of the winding terminal-conductors, or a section on an approximately cylindrical surface indicated by the line II-II of Fig. l, and

Fig. 3 is a fragmentary transverse sectional view on a plane indicated by the line III- III of Fig. l.

I have illustrated my invention in connection with a machine having a direct-current fieldmember or stator 4, and a rotor-member 5, the latter COITIDIiSng an armature-core S, carrying the coils of a direct-current armature-winding 1. which is provided with closely placed insulated terminal-conductors disposed in two concentric, approximately cylindrical groups or layers 9 and lll. The bared terminals ll of these conductors are electrically connected to the necks l2 of successive conducting commutator-bars, which, suitably insulated from each other, constitute the cylindrical commutator-member which is engaged by the carbon brushes, one of which is indicated at I 5.

In accordance with my invention, a number of pieces Il of thin stiff insulating sheet-material, such as "mica or fairly stiff varnish-treated paper, having smooth surfaces, are placed between different pairs of terminal-conductors of the inner cylindrical layer lll, by the Winder, during the winding-process, so as to extend radially inwardly from the inner periphery of said terminal-conductors, at spaced points around the periphery back of the commutator-necks l2. These pieces Il will fit tightly between these terminal-conductors, and they may be placed with one end abutting against the insulation I9 which covers the coil-support 20, as shown in Fig. l. y Preferably, the insulating pieces I1 are preformed with a right-angle bend 2| which is bent or placed over the tops of the terminal-conductors of said inner laye;- I0 before applying the insulating pad 22 between the two layers 8 and l0. The outer layer 9 of terminal conductors is encircled by a retaining band 23 which holds down the inner layer l0 against the insulation I9 on the coil-support 20. In this manner the pieces I1 are firmly held in place.

In operation, in common with al1 other commutator machines, the machine has only small potential-dinerences between adjacent end-winding coil-terminals lll, at the commutator end of the machine, but these potential-differences build up progressively, at successive points around the circumference, until the points are reached corresponding to the brush-position on the commutator l2 at any moment, depending upon the number of poles of the machine.

The coil-terminals l0 are insulated, as shown, and only the extreme ends of the conductors are bare, where they are connected to the necks l2 of successive bars of the commutator. At iirst, these insulated coil-ends ll) present an inner cylindrical surface 25, of clean insulating material, which constitutes no leakage-problem. In time, however, after a considerable length of time during the continued operation of the machine, the carbon-dust from the brushes, (such as the brush I5), tends to accumulate, as a greasy or hard, conducting, encrustation or coating, in a creepage-path, particularly on the inner surface of the inner cylindrical layer I0 of coil-terminals, as indicated in dotted lines 25 in Fig. 3. As shown in this ilgure, my inwardly projecting, smooth surfaced, insulating pieces Il are disposed at sufciently closely spaced points around the periphery to constitute barriers which provide an elongated creepage-path 26 which increases the creepage-distance between terminals of opposite polarity, at least one of said insulating pieces being between terminals of opposite polarity at all times. The pieces l1 also provide a type of smooth surface which does not readily collect carbon-dust. The pieces il also provide sharp-angled pockets, up close to the crusted inner surface 25, Where deposits are not readily accumulated, thus breaking the continuity of the leakage path from a positive brush, as l5, to the next succeeding negative brush. IThus, at a practically negligible cost, I have successfully solved one of the troublesome problems of commutator-machine design.

I claim as my invention:

1. A commutator-type dynamo-electric machine having a cylindrical commutator-meinber comprising a number of insulated conducting bars each having a commutator-neck portion, said machine also having a number of armature-coils having a group of closely placed insulated terminal-conductors disposed in an approximately cylindrical layer and having their bared terminal-ends electrically connected to the necks o! successive commutator-bars, in combination with a plurality of pieces of thin stii insulating sheetmaterial extending approximately radially in- Wardly from the inner periphery of said group of closely placed insulated terminal-conductors, said insulating pieces extending between difierent pairs of said insulated terminal-conductors at sumcently closely spaced points around the periphery to increase the creepage-distance between terminals of opposite polarity, at least one of said insulating pieces being between terminals of opposite polarity at all times.

2. The invention as defined in claim 1, characterized by said insulating pieces being bent over the tops of said insulated terminal-conductors, the machine having encircling means for holding down said bent-over top-ends ci said sheets.

CONRAD WEIL 

